1. Field of the Invention
The present invention generally relates to a phase retardance inspection instrument.
2. Description of the Prior Art
In recent years, the flexible electronics and display related technology has attracted tremendous attention. However, the stress distribution is an important issue due to the use of flexible materials (such as the plastic substrate) as a substrate. Since the substrate is often used when it is warped, cracks of the substrate or the connecting wires due to stress occur to cause damage to the devices. On the other hand, when the plastic substrate that is flexible is used, stress generated during manufacturing processing also causes warping of the display to damage the devices.
Conventionally, the stress of a thin film is inspected by measuring the curvature variation of a glass or silicon substrate before and after it is coated to calculate the stress value. However, when a flexible plastic substrate is used, conventional curvature measurement cannot be used and real-time measurement cannot be achieved for stress monitoring since the curvature variation is too large. Moreover, since the flexible plastic substrate is formed of polymer with birefringence, such as poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN), the stress generated during thin film processing causes the change of birefringence, and the change of phase retardance.
Conventional polarization inspection is performed by rotating polarizing elements or a plurality of polarizing elements to acquire the polarization mode variation. For example, U.S. Pat. No. 6,219,139 “Full field photoelastic stress analysis” filed by Stress Photonics Inc. uses two neutral beam splitters, two polarizing beam splitters, a plurality of polarizing elements, and four image sensors to construct a full field phase retardance stress measurement device.
In U.S. Pat. No. 5,521,705 “Polarized light microscopy” filed by Rudolf Oldenbourg and Guang Mei, a liquid crystal phase compensator is used to replace the conventional phase compensator, wherein the input voltage is adjusted to control the phase retardance value of the compensator to obtain different polarization modes. U.S. Pat. No. 5,521,705 can do without any rotating polarizing element, but the liquid crystal phase compensator does not provide real-time adjustment.